The present invention concerns orthopedic implants, including spinal implants such as intervertebral prostheses and intersomatic cages, for example. Intervertebral prostheses may be implanted between two adjacent vertebrae to maintain or restore a space between the vertebrae while conserving mobility of vertebrae. Intersomatic cages may be implanted between two adjacent vertebrae for placement and growth of bone tissue grafts (or a substitute) in the disc space and to obtain an arthrodesis (the fusion of the two vertebrae). For example, after the cage is positioned, the intervertebral space may be filled with autologous spongy bone or suitable bone substitutes, which may also (or in the alternative) be placed in a cavity in the cage, prior to its positioning in the intervertebral space. In particular, the invention concerns intervertebral implants, implant anchors, the fixation of implants to vertebrae by anchors, and implantation of implants in the disc space by an implantation instrument.
One problem in this field concerns the stability of spinal implants in the disc space once they have been implanted, particularly when an arthrodesis is desired, for example using intersomatic cages or other implants allowing an arthrodesis. For example, there is a risk that the implant will shift in the intervertebral space due to forces imposed when the patient moves, even when the implant is provided with notches or teeth on its vertebral contact surfaces. Therefore it is often necessary to affix the spinal implant to the adjacent vertebrae between which it is implanted. Solutions are known in the prior art that provide the spinal implant with a bone anchoring device that allows solidly attaching the implant into the vertebral endplates of the vertebrae between which the implant is designed to be implanted. Moreover, access to the intervertebral spaces (disc spaces) is often particularly delicate due to the dimensions involved, particularly due to the presence of blood vessels and nerves in the approach to the intervertebral space. Bone anchoring devices must penetrate into the vertebrae with sufficient depth to ensure a good fixation, and must also have a small size and allow affixing the implant without endangering the surrounding blood vessels and nerves (for example, by not requiring more space in the approach to the intervertebral space than necessary for implantation of the spinal implant itself).
In the prior art, notably from published applications FR 2,916,956, US 2009/105832, and WO 2008/149223 filed by the assignee of the present application, which are incorporated herein by reference and to which the reader can refer to examine various problems resolved and various advantages provided by this type of solution, an anchoring device is known, suitable to be implanted solidly and with sufficient depth in the vertebral endplates to ensure that the implant is held tight against these vertebrae, but along an axis of approach for insertion generally in the plane of the intervertebral space. This type of solution typically comprises at least one anchor formed of a curved and rigid plate, arranged so as to penetrate into the endplate of a vertebra through an implant and provided with at least one stop to hold this implant against this vertebra. The rigidity of this type of anchor is an important feature to allow effective fixation, notably more effective than staples or other thin and/or relatively flexible and often fragile devices.
These types of anchoring devices (or “anchors”) comprising a curved plate may pose a problem of the risk of splitting the vertebra during the impaction of the anchors into the vertebra, or due to forces imposed on the implant and/or the anchor once it is implanted in the vertebra. These types of anchors also may present a risk of making a cut that is too large during the impaction of the anchors into the vertebra, allowing the possibility of undesirable play of the anchor, which makes the implant fixation weak and/or unreliable. It should be noted that the term impaction is used here to designate the fact that the anchoring device is driven into the vertebra. It will also be noted that the present application describes an impactor, which is a device for impaction of the anchor because it is arranged to help driving an anchoring device into a vertebra.
Another potential problem of these types of anchors having a curved plate concerns its rigidity. In some circumstances, it is important that the anchor is rigid enough that it will not deform and/or have much play under the effects of the forces that are exerted on it, so that it will not gradually come out of the vertebra in which it is embedded. In addition, passage of the anchor through the implant and maintenance of the stability of such anchor within the implant (subject to an eventual desired play, for instance minimum play) is also an aspect that is important to ensure reliable mounting in some circumstances.